Zimmermann Telegram

(1917)

The Zimmermann Telegram was a coded message, sent between German statesmen in Germany, Washington DC and Mexico in January 1917. The telegram was intercepted in decoded by British cryptographers.
As Germany prepared to resume unrestricted submarine warfare, they feared that the US would be drawn into World War I. If that happened, they hoped to form an alliance with Mexico and Japan. The telegram provided instructions to Germany's ambassador to Mexico who was to propose the alliance and offer to help Mexico reclaim Texas, New Mexico, Arizona and other areas lost during the Mexican-American War.
The revelation of the plot in the American press on 1 March 1917 lead to general outrage and helped overcome US reluctance to enter World War 1.